Many thermoplastics, such as LEXAN.RTM. polycarbonate, require mar-resistant surface coatings to retain transparency under normal operating conditions when used as glazing materials in buildings and in railroad cars, airplanes and the like. A particularly useful family of such coatings are mixtures of silica and hydrolyzable silanes in a hydrolysis medium, such as alcohol and water, see, for example, Misch et al., U.S. Pat. No. 3,708,225; Clark, U.S. Pat. No. 3,986,997 and 3,976,497; and Ubersax, U.S. Pat. No. 4,177,315, as well as in copending application Ser. No. 964,910, filed Nov. 30, 1978. Such coatings are cured thermally, and ultraviolet resistance can be imparted by incorporating a variety of known phenolic ultraviolet (uv) screening agents. These tend to migrate or exhibit plasticizing effects, however, so that silane-functionalization of uv screens, e.g., by forming silylalkyl ether substituents has been developed to insure reaction into the coating composition.
See U.S. Pat. No. 4,278,804 (Ashby et al.); U.S. application Ser. No. 154,621 (Ashby), now allowed, filed May 30, 1980; copending U.S. application Ser. No. 154,625 (Ching), filed May 30, 1980; and U.S. application Ser. No. 154,626 (Ching), now allowed, filed May 30, 1980.
A somewhat more recent development in surface coatings is described in the copending application of Chung, U.S. Ser. No. 129,297, filed Mar. 11, 1980, disclosing ultraviolet light curable silicone hard coating compositions. The various known uv screeners are not effective for such compositions because they retard the curing needed for producing the hardened surface. The foregoing patents and applications are incorporated herein by reference.
It has now been found that functionalized derivatives of precursors of uv screens can be provided, and these will overcome the retardation of uv-curable compositions of the type described in the Chung application. It is further observed that after completion of uv-curing, the precursors will then generate a functionalized uv screen in situ by a photoreaction which is known as a Fries rearrangement. By way of illustration, compound 1 will rearrange to uv-screen 2 as follows: ##STR3##
Entirely analogous to this, the precursors contemplated by this invention, as particularly to be described, will undergo a Fries rearrangement to produce hydroxybenzophenone and hydroxyphenyl phenylsulfonyl uv screens which effectively protect, e.g., poly(bisphenol A carbonate) from yellowing under silicone uv-cured hard coats.